A bug in the R6 firmware announced yesterday has been scrubbed from Canon sites, with users citing camera freezes when using a combination of slow motion frame rates and crop mode. There may be other factors, and additional bugs. A few hours later, they came out with version 1.31, which can be downloaded here.
An attempt by at least one user initially reporting the bug indicated that the firmware is not allowing reversion to the earlier 1.2 version of the firmware.
Camnostic upgraded a couple R5 cameras but not yet the R6 for testing. We will do so later despite the bug in order to better define the circumstances that trigger it. Stay tuned.